This disclosure is related to cleaning of solar cells during fabrication. Solar cells are electrical devices for generation of electrical current from sunlight by the photovoltaic (PV) effect. Each solar cell has one or more layers (thin films) of PV materials such as polycrystalline materials deposited on a substrate. The thickness of the PV materials can be on the order of nanometers or micrometers.
Polycrystalline materials are solid materials composed of many crystallites of varying size and orientation. The variation in direction can either be random or directed, due to various growth and processing conditions. The crystallites are often referred to as crystallite grains or grains, which are formed in the polycrystalline materials when the polycrystalline materials are cooled during fabrication. The areas where these grains meet are known as grain boundaries.
Examples of polycrystalline materials used as absorber layers in solar panels include copper indium gallium selenide (CIGS) and cadmium telluride. Absorber layers absorb light for conversion into electrical current. Solar panels also include front and back contact layers to assist in light trapping and photo-current extraction and to provide electrical contacts for conducting the generated current across the solar panel. The front contact typically comprises a transparent conductive oxide (TCO) layer. The TCO layer transmits light through to the absorber layer and conducts current in the plane of the TCO layer. In some systems, a plurality of solar cells are arranged adjacent to each other, with the front contact of each solar cell conducting current to the next adjacent solar cell.